Facile one-step deposition of ZnO-graphene nanosheets hybrid photoanodes for enhanced photoelectrochemical water splitting

Abstract

ZnO-graphene nanosheets photoanodes were deposited at room temperature by a one-step kinetic spray process on a titanium sheet from micro-sized ZnO and graphite powders. ZnO-graphene nanosheet hybrid photoanodes with varying graphite contents were utilized for studying photoelectrochemical (PEC) water splitting. The Raman spectra revealed the direct transformation of micro-sized graphite powder to graphene nanosheets in all hybrid photoanodes after the deposition process, without any post-treatment. Surface morphology analysis revealed the fragmentation of the micro-sized flake morphology to morphology composed of mixed nanorods and nanosheets. The optical properties of the ZnO-graphene nanocomposites were investigated by the diffuse reflectance and photoluminescence (PL) emission spectroscopy, which revealed the decrease of the optical band gap and quenching of PL intensity. The hybrid photoanode with 50 wt% graphite content revealed the smallest bandgap of 2.6 eV and the lowest emission intensity compared with other hybrid photoanodes, which demonstrated the inhibition of photogenerated charge carrier recombination rate as well as an improvement in the visible-light-harvesting. The PEC results exhibited an improvement of the photocurrent with the incorporation of graphene nanosheets due to the improved photogenerated charge transfer kinetics and separation. The hybrid photoanode with 50 wt% graphite content revealed the highest photo-response current of 4.82 mAˑcm−2 corresponds to photoconversion efficiency of 3.25% @1.23 V vs. RHE.